Market cap is related to how many bitcoins are already in existence * current price. It doesn't have to do with where the transactions are being made.

It does, as off exchange transaction do not have a influence on the exchanges rates, which is what determines the price currently.

It also doesn't mean that the buyers buy at exchange rates. For large quantities it may be well below or above current rates, depending on wheter the seller or the buyer is desperate to get rid of or to get the coins.

It does, as off exchange transaction do not have a influence on the exchanges rates, which is what determines the price currently.

Off exchange transactions does influence price on the exchanges. People begin arbitraging as soon as the gap in price between on and off exchange begins to widen, which then brings the price to similar levels again.

Market cap is related to how many bitcoins are already in existence * current price. It doesn't have to do with where the transactions are being made.

It does, as off exchange transaction do not have a influence on the exchanges rates, which is what determines the price currently.

All trading of bitcoins for other things affects the price whether it is done through an exchange or not because the supply and demand are still affected. Localbitcoin trades are off-exchange, but it would be wrong to assert that localbitcoin trades to not affect supply and demand and therefore do not affect the price.

What does it mean to be off-exchange, anyway? Suppose Bitstamp stopped publishing trade information. Would that make them off-exchange? You could even consider off-exchange trades to be on an informal decentralized exchange because buyers and sellers still meet and negotiate prices.